Factors that affect the growth of precursor populations can directly impact the size of their tissue derivatives, including the functions referable to the organ systems that they help to form. Cortical precursors from the embryonic rat telencephalon display differential growth characteristics, a property which suggests that the growth potential of some precursors is restricted long before neuronal precursors begin to differentiate. These precursors are notable for their expression of a recently described membrane protein, R-prominin, whose function is unknown. We predict that R-prominin is involved in the control of cortical precursor proliferation. Using adenoviral gene transfer methods and recombinant fusion proteins for R-prominin, our studies will examine the mechanisms that effect the proliferation potential of cortical precursors. Specifically, we will examine the relationship between R-prominin expression and alterations in cell-cycle status. Our studies will reveal information about the signaling pathways involved in the control of cortical precursor growth and differentiation.